For example, aluminum-based metal materials have a dense and firm oxide film on the surface. Due to this offending oxide film, it is difficult to join such aluminum-based metal materials by a metallurgical method.
For example, Patent Literature 1 describes a method of joining aluminum to aluminum or aluminum to alumina, including: intervening an insert between faces to be joined wherein the insert includes an element that reacts with the base material to cause eutectic reaction, making them in contact with each other in an oxygen atmosphere, and then heating the faces to be joined to a temperature in the range that effects the eutectic reaction, so as to produce a melt phase on the contact face due to the eutectic reaction as well as an oxide phase due to a reaction between the components of the base material and oxygen present at the gap of the contact face (see claim 1). As a result, it is described that the oxide film on the surface of the base material is broken and mixed in the melt phase along with the oxide produced by a reaction between the components of the melt phase and oxygen (see a middle part of the left column on page 3).
Another joining technique for aluminum-based metals known in the art is brazing by an Al—Si brazing alloy. However, this method requires removing the oxide film by using, for example, a fluoride flux.